The present invention relates generally to the field of apparatus for fiber optic communication, and more particularly, to limited rotation fiber optic rotary joints to provide transmission of an optical signal through a mechanically rotational interface for a limited number of rotations.
An optic device to transmit optic signal from a rotating member to a stationary member is called fiber optic rotary joint (FORJ). There are many different types of fiber optic rotary joint. They can be a single-channel, multi-channel, hybrid (two different types of signals), etc. Fiber optic rotary joints can be generally categorized as either limited or unlimited rotation. A limited rotation FORJ can be rotated a maximum number of times in each direction. Conversely, the number of rotations of an unlimited rotation FORJ is bounded strictly by the life of the unit. For example a limited rotation FORJ with a maximum of 500 rotations may have a life of 10,00,000 rotations but can only be rotated 500 turns either clockwise or counter-clockwise before it has to rotate in the opposite direction. However, an unlimited rotation FORJ with a life of 10,000,000 rotations can be rotated clockwise, counter-clockwise or any combination of the two for a total of 10,000,000 rotations.
While the unlimited rotation fiber optic rotary joints have the obvious benefit of far more rotations in either direction, this benefit comes at a cost. That cost is unusually a significantly more complex design which results in higher signal loss, lower device reliability. If the number of rotations in a given direction is known, for example a tow-array reel with 100 meters of cable, then a limited rotation FORJ can be design for the number of turns necessary to unspool 100 meters of cable. In this and similar applications where the benefit of an unlimited rotation FORJ would not be realized making the limited rotation FORJ with its higher reliability connection and lower signal loss a better and quit often less expensive option.